Conventional thermally conductive composites contain high thermal conductivity particle fillers in a matrix. In these conventional composites, particle fillers such as alumina, metal powders, and boron nitride are added to materials such as silicone rubber, polyamide, and polyester. Particle filler content is typically very high, 50% or even higher. The resulting composite materials have thermal conductivities on the order of 5 W/m-K.
The development of the high-pressure carbon monoxide (HiPCO) process of fabricating nanotube materials allows production of 1 gram/hour of single-wall nanotube (SWNT), inviting nanotube applications requiring industrial quantities. It is expected that good thermal conductivity, electrical conductivity, and/or mechanical stiffness can be realized by proper incorporation of nanotubes in polymer composites.
Nanostructures, such as single-wall carbon nanotubes (SWNT), are extremely promising for enhanced stiffness in mechanical composites, as they provide a high Young's modulus and strength-to-weight ratio. Such lightweight and strong polymers are expected to find considerable utility in the automobile and aerospace industries, among others. Also, because phonons dominate thermal transport at all temperatures in nanotube materials, nanostructures appear ideal for high-performance thermal management.
Similarly, epoxy resin-nanotube compositions have been prepared with the hope of obtaining composites of high mechanical strength. However, nanotube-epoxy composites previously manufactured have typically been weaker or only slightly stronger than the pristine epoxy (Vaccarini et al. Proceedings of the XIV International Winterschool, p.521; 2000; Ajayan et al. Advanced Materials 12, p.750; 2000; and Schadler et al. Appl. Phys. Lett., 73, p.3842; 1998). Enhanced strength has been observed in SWNT-PMMA (polymethyl methacrylate) composites (Haggenmueller et al. Chem. Phys. Lett. 330, p.219; 2000); however the composites did not display the enhanced stiffness predicted by simple models of polymer/nanotube composites. Thus, despite the great promise of nanotube composites, the properties obtained to date have not met their apparent potential. One possible factor contributing to this disappointing performance is poor dispersion of the nanotubes in the polymer matrix.
There continues to be a need for methods of incorporating well-dispersed nanotubes into polymeric materials to provide composites having good thermal, electrical, and/or mechanical properties.